A Passive Optical Network (PON) provides very high-speed services to businesses, small office home offices (SOHOs), and homes, through optical fibers, and has such a name because it constitutes an optical communication network with passive elements. Generally, in a PON, an optical line terminal (OLT) is installed in a central office, and a plurality of Optical Network Units (ONUs) are connected to the OLT via a 1:N optical star coupler. Such a PON is classified into a Broadband PON (B-PON), a Gigabit PON (G-PON), and a Gigabit Ethernet PON (GE-PON).
The B-PON is aimed at receiving all existing electrical communication services, and transmitting data signals by allocating them to Asynchronous Transfer Mode (ATM) cells. The G-PON, like the B-PON, is aimed at receiving all electrical communication services, and adopts a G-PON Encapsulation Method (GEM) to efficiently receive Ethernet frames. Since GEM frames can be defined by the same time unit as that used in existing electrical communication services, the GEM frames can be efficiently used for existing services using telephone lines or private lines.
The GE-PON, which is also called an E-PON, has an advantage of high-speed data transmission, and allows transmission of high quality Internet Protocol (IP) images, IP telephony, and video phone services. The B-PON, G-PON, and GE-PON have been standardized by the ITU-T and IEEE.
The G-PON stores and transmits uplink data using a plurality of class queues that are called transmission containers (T-CONTs), for each service, in order to allow ONUs to receive various types of traffic.
Also, an OLT collects wait state information of all T-CONTs that operate on a link, and allocates an uplink bandwidth to each T-CONT on the basis of the wait state information. Specifically, the G-PON allows each ONU to transmit uplink frames in units of a frame of 125 us, in order to support voice services, etc. having strict delay conditions.
As such, in order to improve the efficiency of a network and guarantee transmission quality when ONUs transmit uplink data, dynamic bandwidth allocation is needed which calculates an uplink bandwidth of each T-CONT for each frame on the basis of service level agreement (SLA) and wait state information of the T-CONT.
A conventional dynamic bandwidth allocation method has been developed which allocates a predetermined bandwidth to T-CONTs, on the basis of a bandwidth allocation period and a bandwidth allocation amount for each T-CONT that are calculated by SLA of the T-CONT, regardless of wait state information of the T-CONTs. In the conventional method, since a bandwidth is allocated to each T-CONT regardless of the T-CONT's wait state information, an uplink bandwidth is allocated to the T-CONT even when no data waiting for uplink transmission exists in the T-CONT, which causes an unnecessary waste of bandwidth.
Another conventional dynamic bandwidth allocation method has been developed in which bandwidths are allocated to all ONUs under the same service condition. In order to uniformly allocate bandwidths to a plurality of ONUs requiring allocation of bandwidth, an uplink bandwidth is divided by the number of ONUs.
Then, the resultant bandwidth (that is, an additional bandwidth) is compared with a bandwidth required by each ONU, and bandwidths required by ONUs are allocated to the ONUs if the ONUs require bandwidths smaller than the additional bandwidth, and an additional bandwidth is allocated to ONUs requiring bandwidths greater than the additional bandwidth.
However, in this conventional method, since bandwidths are allocated to a plurality of ONUs requiring allocation of bandwidth, the unnecessary waste of bandwidth as described above is avoided. However, if any bandwidth remains after bandwidths are allocated to the plurality of ONUs, the remaining bandwidth will be discarded without being used.